1. Field of the Invention
An embodiment of the invention generally provides a telescoping mast for supporting and raising a load. More particularly, an embodiment provides a telescoping mast, which is capable of being locked into a generally rigid formation along a range of telescopic lengths, and which is telescopically extended by a zipper-action chain extension system further comprising a system for the management of one or more cables.
2. Description of Related Art
Collapsible masts are well known in the art, and generally provide the ability to raise and lower a load mounted thereon from some minimum height, when the mast is in a collapsed configuration, to a desired elevation, but not higher than the maximum extension height of the mast. While it should be obvious to one of ordinary skill in the art that such a mast can be used to extend horizontally, or in other directions with respect to the ground, telescoping masts will generally be discussed herein as extending vertically, i.e., raising (upward) and lowering (downward) with respect to the ground.
In the collapsed, fully lowered configuration, the mast occupies significantly less space than when extended. The lowered position generally also provides a lower center of gravity for the load. Thus, in the collapsed position there is generally a reduced lever force exerted by the load through the mast against the base of the mast as compared to the forces exerted by the load when in the extended position. On a vehicle-mounted mast, the load will generally experience forces that tend to rotate it and the top of the mast relative to the base thereof, due for instance to an uneven or non-level route of travel. Therefore, for a vehicle-mounted mast, the reduced lever force achieved in the collapsed position can be highly beneficial during transport.
In the raised position, the mast may elevate the load above nearby objects that would otherwise interfere with operation of instruments that comprise the load, such as by interrupting a necessary line-of-sight between the instruments and a more distant location. For instance, it is common for trucks used by mass media production companies (e.g., news trucks) to utilize a telescoping mast to raise broadcast antennas. Military forces also make use of masts mounted on vehicles, for instance, to provide for artillery observing. Forward observer vehicles will often include an array of targeting instrumentation on a mast, which can be raised to allow the instruments to “see” over concealing terrain such as a berm or brush. The mast, therefore, can be utilized as an aid to provide for more accurate observing and targeting, while still allowing the observers in the vehicles to be more protected from enemy sight.
One type of collapsible mast which is useful in this situation is a telescoping mast wherein the mast comprises a series of interlinked sequentially nesting segments, each one generally having a smaller circumference and cross-sectional area than the prior segment in the sequence. When collapsed, the telescoping mast will have the various mast segments arranged one inside the other in a nested arrangement. Therefore, in the collapsed position, the external shape and size of the mast may only be as large as its largest segment.
This telescoping mast is extended by moving the segments out from inside each other, which when fully extended produces a tapered, hollow pole. Generally, the smaller internal mast sections will extend to a higher elevation to keep the center of gravity of the mast lower, but that is by no means necessary. For ease of discussion, telescoping masts herein will be assumed to extend with the smaller internal segments being extended upward from within the larger segments. One of ordinary skill in the art would understand how to utilize the devices discussed herein on masts that extend in an alternate manner.
Once a telescoping mast is extended, the segments must be held in their relative extended positions to support the raised load which is at the top of the mast. In a basic design, the mast is extended by a drive device, such as a motor, which can then hold the segments in place in an extended position by utilizing a lock on the motor that prohibits collapse of the drive mechanism, or similarly by maintaining motor braking to continuously support the mast in the extended position.
Such systems utilizing only the drive mechanism to maintain the mast at an extended position generally do not produce as stable a mast as one in which the segments are securely connected together when extended. Securely connecting segments are often called “locking” a mast. Such connection may be achieved through at least a couple of methods. In one, each of the mast segments is tapered slightly with the wider and narrower ends arranged at the same relative ends of each mast segment. As the inner segments extend relative to the outer segments, the wider end of the smaller segment is moved toward the narrower end of the larger segment. These two segments are sized and shaped so that the smaller segment's wide end is slightly wider than the larger segment's narrow end. In this arrangement, the ends of adjacent segments will contact and be forced into a frictionally tight fit. This frictional fit provides for rigidity between the two segments by effectively forming the segments into a single interconnected structure. The problem with this design is discovered upon collapsing the mast. The stronger the connection between the segments when extended, the more force required to separate the segments to collapse the mast. Further, as pieces become worn, the frictional connection strength will be decreased and the mast becomes less rigid. For these reasons, this design is rarely used on large commercial masts.
In an alternate design, the segments have straight, non-tapered sides, and include a locking mechanism. These segments have a locking actuator fixed in position at both an upper position and a lower position, which positions generally closely correlate with the top and bottom of a segment. In this alternate design, a pair of locking rings circumscribes each segment (except the most outer one). Each ring freely floats between two segments, until it becomes compressed between the actuators of adjacent segments as those segments are extended relative to one another. At a certain extension, the actuators begin to force the two rings against the surfaces of the adjacent segments causing the segments to frictionally engage each other via the rings. This system is generally easier to disengage than the frictional fit of tapered segments.
Both the methods discussed above are efficient for providing a relatively rigid resultant mast, but both are limited by requiring the resultant mast to have a fixed extension at which the locking mechanism is engaged. This means that the mast generally has only two stable positions, a lowered position where it is fully collapsed, and a raised position where it is fully extended and the locks are engaged. As discussed above, while the lift drive could stop the extension at any intermediate point, such an intermediate position is not as stable as either of the fully extended and locked or the fully collapsed positions. It has generally not been possible to lock the mast at an intermediate height, since the prior art shows the locking actuators in fixed positions on the various segments.
An additional problem encountered with prior art collapsible masts is that cables, such as power and communication cables, that are routed generally from the base of the mast up to the load at the elevated end of the mast are a challenge to manage, and may require complex apparatuses to ensure that the cables are not entangled in the mast components or other nearby equipment, particularly during collapse of the mast. Without such a complex cable management apparatus, a user has been left to bear the risk of entanglement.